There is force control which controls a position and a contact force in an operational coordinate system while an endpoint such as an endpoint part of an arm of a robot (hereinafter, simply referred to as “endpoint”) is in contact with a target object. In the force control, it is important to estimate an external force applied to the endpoint and to flexibly correct motion responsive to the external force.
In order to quickly and securely follow a force and a moment in contact, an integral compensator is provided between the endpoint and the operation target object. Integral compensation is applied to an output from a compliance model, such as a spring-mass damper model (JP-A10-193290 (Kokai)).
However, for instance, in a case where an operation target object has not been accurately positioned and the endpoint does not contact at an assumed position, contact force is not generated. Accordingly, there is a possibility that the endpoint continues to operate. In contrast, there is a possibility that the endpoint contacts the operation target object before reaching a target position and thereby causes an excessive contact force. In general, force control is inferior in responsiveness to position control. The force control has a slower following speed to the target contact force. In order to improve operation efficiency, it is necessary to promptly find an error and immediately transition to a retry operation. It is difficult to improve responsiveness only by monitoring deviation from a target value.